The moves are "reflective of a price war," said David Heger, senior equity research analyst with Edward Jones.

Actually, a price war has already been going on for a couple years now, he said, with T-Mobile ending two-year contracts nearly four years ago. AT&T, T-Mobile and Sprint began focusing on unlimited data plans in August 2016, targeting consumers who use a lot of data on their smartphone.

"Verizon was sitting out there as the only one that didn’t have an offering," Heger said.

Verizon, the nation's largest wireless provider, quit offering an unlimited plan to new customers in 2011. It returned to the unlimited game Monday, announcing the move to consumers with TV ads during Sunday's Grammy Awards broadcast.

T-Mobile counters

It didn't take T-Mobile's CEO John Legere long to respond. Legere, who jumpstarted the move toward unlimited data plans and isn't shy about attacking the biggest carriers for their pricing, announced that customers on T-Mobile's $70 unlimited T-MobileOne plan will get HD video and up to 10GB of high-speed "hotspot" data at no extra cost, taxes and fees included. Added promotion for a limited time: two lines cost just $100.

And Legere tweeted a customary dig: "No shock that @verizon finally decided to show up. And I don't blame them for caving. What choice did they have?"

"Verizon has always positioned itself as the premium player with the best network," Heger said. "The pricing they have set up reflects that."

Verizon says it rolled out the unlimited data plan because its network can handle the influx of customers and "we fundamentally want you to have more choice," said Ronan Dunne, president of Verizon’s wireless division.

That superior network remains a competitive advantage for Verizon, even though competitors have closed the gap, said CFRA Research analyst Angelo Zino. Verizon's move to unlimited "may help prompt current subscribers from looking elsewhere for those options,"he said.

Carriers' embrace of unlimited data could have other repercussions in the marketplace. Some Wall Street analysts point to Dish Network, which holds wireless spectrum capacity, as a possible acquisition for Verizon. Others have rumored that Verizon might seek to merge with Charter, which itself acquired Time Warner Cable in October, to gain additional wireline capacity. "I think they have to be looking at a lot of strategic options," Heger said.

Comparing unlimited data plans can be complicated. For instance, Sprint is currently running a limited time promotion that offers unlimited talk, text and data for $50 per month for one line or $90 monthly for five lines. Like Verizon and AT&T, Sprint's price does not factor in taxes and fees. T-Mobile charges $70 for its unlimited plan (for one line; $160 for four lines) but includes all the taxes and fees.

With Verizon, "the fine print on the offer makes it slightly less aggressive than it would initially appear," Vijay Jayant, an analyst with Evercore ISI, in a note to investors Monday. That's because corporate and group discounts do not apply and customers must sign up for paperless billing and AutoPay, using a checking account or debit card. That saves Verizon 2% to 3% in fees, Jayant says.

Like competing plans, Verizon's unlimited plan has a "soft cap" -- Verizon's is 22 Gigabytes per month -- after which usage could be slowed and prioritized for overall network efficiencies. T-Mobile also had streamed most video via unlimited plans at standard definition quality, but now plans to match Verizon promise of HD video. Sprint charges for HD video under its premium unlimited plan, which at $70 monthly for one line is cheaper than Verizon's plan.

And as with all new plan promotions, new and current customers can also get free smartphones with a trade-in by moving to Verizon's unlimited plan (with a monthly charge for the phone being offset by a monthly credit for the trade-in).